Geared rotary actuator

ABSTRACT

A geared rotary actuator has a differential gear unit having a drive input and first and second outputs, an output driven member for connection to an external member to be driven by the actuator and first and second drive paths ( 200, 300 ) coupling the first and second outputs of the differential gear unit to the output driven member. Under normal conditions, drive is transmitted from the input drive to the output driven member via the differential gear unit ( 100 ) and the first drive path ( 200 ). However, if the first drive path ( 200 ) jams, drive is transmitted to the output driven member via the differential gear unit ( 100 ) and the second drive path ( 300 ). If the differential gear unit ( 100 ) jams, drive is transmitted to the output member ( 36 ) via the differential gear unit ( 100 ) and both the first and second drive paths. The gear ratio between the drive input and the output driven member remains substantially constant.

The present invention relates to a geared rotary actuator.

Geared rotary actuators are used in, for example, aerospace applicationswhere they may be used in driving aircraft control surfaces, bay doorsand the like.

The present invention seeks to provide an improved actuator.

Accordingly, the present invention provides a geared rotary actuatorhaving:

a differential gear unit having a drive input and first and secondoutputs;

an output driven member for connection to an external member to bedriven by the actuator;

and first and second drive paths coupling said first and second outputsof the differential gear unit to said output driven member;

wherein:

the arrangement is such that under normal conditions drive istransmitted from the input drive to the output driven member via thedifferential unit and the first drive path;

in response to jamming or binding of said first drive path drive istransmitted to said output driven member by way of said differentialunit and said second drive path;

and in response to jamming or binding of said differential unit drive istransmitted to said output member via said differential unit and bothsaid first and second drive paths;

the arrangement being further such that the gear ratio between saiddrive input and said output driven member remains substantially thesame.

In a preferred form of the invention the second drive path has an outputcarrier member which carries the whole of the first drive path such thatin response to jamming of said first path the whole of the primary pathis caused to rotate on block thereby to transmit drive to the outputdriven member.

Advantageously, each of the first and second drive paths include abalanced planetary configuration to reduce the tendency of the planetsto skew under applied loading.

The present invention is further described here and after by way ofexample, with reference to the company drawings, in which:

FIG. 1 is a perspective view, past section, of a preferred form ofactuator according to the present inventions;

FIG. 2 is a part sectional view along the longitudinal axis of theactuator of FIG. 1;

FIG. 3 is a simplified, diagrammatic view, similar to that of FIG. 2 ofthe actuator of FIG. 1; and

FIGS. 4 to 6 are diagrammatic representations of the effects of variousparts of the actuator jamming.

Referring to the drawings, these show a preferred form of geared rotaryactuator 10 which has a drive shaft 12 coupled to an output member 36 byway of an input differential gear unit 100 and two drive paths, aprimary drive path 200 and a secondary drive path 300, which areillustrated in simple form in FIG. 3. The two drive paths are compoundplanetary epicyclic gearing, each of which is driven by an output of theinput differential gear unit 100. The first drive path is the main ornormal drive path through which drive is transmitted from the driveshaft 12 to the output member 36.

However, if this drive path becomes jammed, drive is transmitted to theoutput member 36 via the secondary drive path 300. The secondary drivepath has an output carrier 302 which carries the whole of the primarypath and causes it to rotate en bloc. Ratios of the input differentialgear unit 100 and the individual drive paths are selected such that inthe event of binding or jamming, the output member 36 continues torotate at substantially the same speed relative to the input. Thisoccurs regardless of the drive path taken within the actuator. If theinput differential gear unit 100 itself becomes jammed the input driveis passed to both the primary and secondary drive paths which are summedsuch that the final ratio between the input and output of the actuatoris substantially unchanged. As a result, the output member 36 is drivenat substantially the same speed relative to the input drive.

The preferred form of the actuator 10 is now described below in moredetail.

The drive shaft 12 is mounted for rotation by bearings 14, 16 which aresupported on sleeves 18, 20 splined to the drive shaft 12 adjacentrespective end regions 22, 24. The end region 22 is splined forconnection to a drive source whilst the end region 24 is also splinedfor connection to a further actuator or the like. It will be appreciatedthat the splined end region 24 may be dispensed with.

The drive shaft 12 is supported by the bearings 14, 16 in respective endplates 26, 28 of the actuator.

The end plates 26, 28 are generally circular and the end plate 26carries a cylindrical extension 30 which extends toward the end plate28. Supported between the end plate 28 and the cylindrical extension 30is an earth or reaction member 32, the carrier member 302 and the outputor drive member 36. The reaction member 32 is generally cylindrical andcarries a foot or support 38 by means of which it may be secured toprevent its rotation relative to the end plate extension 30. The outputor drive member 36 is also cylindrical and carries a foot or extension40 for connection to an external driven member. The reaction member 32and the output member 36 are in the form of ring gears having teethformed on their radially inner surfaces.

The carrier 302 has a radially inner sleeve 304 which coaxiallysurrounds a central portion of the drive shaft 12 and is spacedtherefrom by an intervening tubular sleeve 102 of the differential unit100. The drive shaft 12, sleeve 102 and sleeve 304 are coaxial andmounted for relative axial rotation.

The carrier 302 has a radially outer cylindrical wall 306 formed bythree axially spaced cylindrical portions 306 a, 306 b and 306 c. Thesewall portions are axially spaced from one another with the cylindricalwall of the reaction member 32 lying between the carrier wall portions306 a and 306 b and the output cylindrical member 36 lying between thecarrier walls 306 b and 306 c. The arrangement is such that the endplate extension 30, the carrier wall portions 306 a, 306 b, 306 c, thereaction member 32 and the output member 36 all form a generallycylindrical unit whose radially outer surface effectively forms acylindrical housing of the actuator 10.

The members 32, 36 and the wall portions 306 a, 306 b and 306 c all havea common axis of rotation with the drive shaft 12 and the sleeve 102.The members 32 and 36 are rotatable relative to one another and to thewall portions 306 a, 306 b and 306 c as is explained further below.

The wall portion 306 b is formed integrally with the sleeve 304 whilstthe wall portions 306 a and 306 c are formed by cylindrical memberssplined to respective ends of the sleeve 304. This is to facilitateassembly.

The actuator input differential unit 100 comprises a coaxial gear wheel104 formed on the drive shaft 12 adjacent the end plate 26. The gearwheel 104 engages with a number of planetary wheels 106 which arepreferably equi-angularly spaced about the axis of the drive shaft 12.Ideally there are three planetary gears 106 and these are supported onrespective radial extensions 108 on the sleeve 102. The gears 104 and106 of the differential gear unit 100 reduce the input drive speed by apreselected ratio.

The primary drive path 200 is described first below.

As is mentioned earlier, one output of the input differential gear unit100 transmits drive from the drive shaft 12 to the primary drive path200 of the actuator 10.

The planetary gears 106 of the differential unit 100 at the drive end ofthe drive shaft 12 engage a reduction gear 110. The reduction gear 110is formed by inner and outer rings 112, 114 which are rigidly connectedand which extend in opposite axial directions. The outer ring 114 hasinwardly facing gear teeth which engage the planetary gears 106. Theinner ring 112 has outwardly facing gear teeth which engage an number ofplanetary gear units 202. Each gear unit 202 has an outer and inner gearwheel 204, 206 rigidly mounted on a common shaft 208 for rotationtogether. The outer gear wheels 204 engage the inner ring 112 of thereduction gear 110.

The inner gear wheel 206 of each gear unit 202 is coupled to severalfurther planetary gear units 210 by way of a reduction gear 212.

The reduction gear 212 is formed by inner and outer sleeves 214, 216which are rigidly interconnected and which extend in opposite axialdirections in a similar manner to the reduction gear 110. The innersleeve 214 is coaxially mounted on the carrier sleeve 304 for relativerotation and carries radially outer gear teeth for meshing with the gearunits 210. The outer sleeve 216 has radially inwardly directed teeth formeshing with the gear wheels 206 of the planetary gear units 202.

The form of actuator 10 illustrated in the drawings has six planetarygear units 210 meshing with the gear wheel 214. Although the number ofplanetary gear units 210 can be varied, the units are preferablyequi-angularly spaced about the drive shaft 12. Advantageously, morethan six planetary gear units 210 can be included and, ideally, betweenseven and nine would be provided.

Each gear unit 210 consists of three gear wheels 218, 220 and 222rigidly secured to or integral with a common shaft 224. The three gearwheels 218, 220 and 222 are axially spaced apart by lands or reduceddiameter portions 226 of the shaft.

A balanced planet configuration is used here to reduce the tendency ofthe gear units 210 to skew under the applied loading. This entails theuse of three planet/annulus gear meshes for the primary (and thesecondary) drive path. Ideally the end gear wheels 218, 222 areidentical or nearly identical so that the forces thereon aretheoretically balanced, causing minimal tendency for skewing of the gearunits 210 about their longitudinal axes.

The gear units 210 are supported on two support rings 50, 52 which aremounted coaxially with but radially spaced from the carrier sleeve 304.The support rings 50 loosely engage the respective lands 226.

The gear wheels 218 and 222 of each gear unit 210 mesh with gear teethon the radially inner surfaces of the carrier wall portions 306 b & 306c. The gear wheel 220 meshes with teeth on the radially inner surface ofthe output member 36. The gear wheel 218, in addition, meshes with thegear wheel 214.

As can be seen particularly from FIG. 2, the support rings 50 assist inmaintaining the gear wheels 218 and 220 in engagement with the carrierwall portion 306 b and the output member 36 whilst maintaining asuitable radial spacing of the gear unit 210 from the carrier sleeve304.

Referring now to the secondary drive path 300, the opposite end of thesleeve 102 carries an integral gear 116 forming the second output of theinput differential gear unit 100. The gear 116 meshes with a number ofplanetary gear units 310. The gear units 310 are preferably identical tothe gear units 202 but need not be identical. Each gear unit has aninner gear wheel 312 and an outer gear wheel 314. The gear wheel 116engages with the outer gear wheel 314 of each gear unit whilst eachinner gear wheel 312 engages with several further planetary gear units316 by way of a reduction gear.

The gear units 316 are shown identical to the gear units 210 althoughthis is not necessarily the case. Each gear unit 316 has three gearwheels 320, 322 and 324 rigidly mounted on or integral with a commonshaft 326 with the gear wheel 324 meshing with gear teeth on a radiallyinner wall of the wall portion 306 b and the gear wheel 322 meshing withgear teeth on a radially inner wall of the reaction member 32. The gearwheel 320 of each unit 316 is coupled to the gear wheels 312 in the samemanner as the gear wheels 218 are coupled to the gear wheels 206, by wayof a reduction gear 318 which is similar to or identical with thereduction gear 216.

The gear units 316 are supported by support rings 50 in the same manneras the gear units 210.

As will be appreciated from the above description, in the main drivepath the drive is transmitted from the drive shaft 12 to the firstoutput of the differential unit 100 through the planetary gear wheels106 and the gear member 110, and then through the planetary gear units202 and the planetary gear units 210 to the output member 36.

Under normal operating conditions drive from the drive shaft 12 istransmitted along this drive path to the output member 36.

Drive from the drive shaft 12 to the output member 36 along thesecondary drive path is transmitted to the second output of thedifferential unit 100 via the sleeve 102, the gear wheel 116 and thenthrough the gear unit 310 reduction gear 318, gear wheel 320, thecarrier 306 and the gear units 210 to the output member 36.

The operation of the actuator is now described below particularly withreference to FIGS. 4 to 6.

As is mentioned above, under normal operating conditions drive istransmitted from the drive shaft 12 to the output member 36 via the maindrive path. If, however, this main drive path becomes jammed, forexample as a result of one or more teeth being broken off from one ofthe gear wheels and causing any of the gear wheels in this path to lock,drive is transmitted to the output member from the drive shaft 12 alongthe secondary drive path.

It will also be advisable to include a shear neck device, or similararrangement (not shown), to ensure that drive is through the primarydrive path unless jamming of the right hand or primary drive path shouldoccur, in which case drive is diverted to the secondary drive path.However it may be necessary for the secondary drive path to be checkedas functional using test equipment. For this purpose a brake or brakesmay be used for operation to check the drive paths are functional.

If the differential gear jams such that the gear ratio across thedifferential is 1:1 as opposed to the normal reduction gear ratio thendrive from the drive shaft 12 is transmitted along both the primary andsecondary drive paths to the output member 36.

Each compound planetary epicyclic gearing of the actuator primary andsecondary drive paths has a substantially different ratio to account forthe differing ratios of the input differential along each particulardrive path. These are selected along with the input differential andother gears to give a substantially constant ratio between input andoutput regardless of the drive path taken within the actuator.

The above will be explained in more detail. A simple differential gearhas two outputs. If one output of the differential gear is “earthed” andthe other is coupled to a reduction gearbox with an output, drivenmember, if the reduction gearbox or the differential jams then drive tothe output member is lost. In the illustrated embodiment of the presentinvention, under normal operating conditions the second output of thedifferential gear is earthed by way of the secondary drive path. Thus,as is simply illustrated in FIG. 4, a clockwise rotation of the driveshaft will produce an anti-clockwise output at a reduced speed accordingto the differential gear ratio. If we assume that this differential gearratio is, for example, 3:1 then the reverse drive output of thedifferential is represented as −3:1. This is applied to the outputmember 36 along the main drive path to provide an output having aclockwise direction of rotation. If the gear ratio along the main drivepath is chosen at, for example, 40:1 then the transform from thebeginning to the end of the main drive path is represented as −40:1. Thegear ratio from the input to output rotational speed of the outputmember 36 is given by the equation: $\quad \begin{matrix}\quad & \omega_{out} & {= {{\omega_{in}\left( {{- 1}/3} \right)}\left( {{- 1}/40} \right)\quad {rpm}}} \\{{where}\text{:}} & \omega_{out} & {{{is}\quad {the}\quad {output}\quad {member}\quad {speed}},{and}} \\\quad & \omega_{in} & {{is}\quad {the}\quad {input}\quad {drive}\quad {speed}} \\{{Assuming},{{for}\quad {example}},} & \omega_{in} & {= {1000\quad {rpm}}} \\{then} & \omega_{out} & {= {{25/3}\quad {rpm}}}\end{matrix}\quad$

If, however, the main drive path jams then drive to the output member 36is transmitted along the secondary drive path to the output member 36.Thus, the output drive from the differential is in the same direction(clockwise) as the drive shaft 12. However, the differential ratio isdependent on the drive path taken and the arrangement of the feedbackpath along the jammed main drive path to the differential affects thegear ratio of the differential in this mode. Since drive to the outputmember along the secondary drive path will be via the gear units 316,the carrier 306 and the gear units 210, some drive will be transmittedvia the gear units 202 back to the differential gear unit 100 toinfluence the differential gear ratio.

The input drive and output along the secondary drive path are both inthe same direction as the drive to the drive shaft 12 and if we assumethat the feedback to the differential gear results in a differentialratio of, say, 4:1 then the arrangement of gears along the secondarydrive path are chosen such that the gear ratio along the secondary drivepath is 30:1. Thus, the rotational speed of the output member 36 isgiven by the equation: $\begin{matrix}{\omega_{out} = \quad {{\omega_{in}\left( {1/4} \right)}\left( {1/30} \right)}} \\{= \quad {{25/3}\quad {rpm}}}\end{matrix}$

Because the output carrier 306 carries the whole of the primary drivepath the latter is caused to rotate en bloc. This causes the normaloutput of the differential gear unitl 100 to be “back-driven” thusapplying a rotation at the differential which affects the differentialgear ratio between input and output. This needs to be accounted for inthe selection of the gear tooth numbers of the reduction gears so thatthe requirement for a substantially constant ratio between the input andthe output of the actuator are met.

Looking now at FIG. 6, if the differential itself jams then the gearratio across the differential is 1:1 with the output drive in the samedirection as the input drive. However, in this case drive is transmittedto the output member 36 along both the main and secondary drive pathsand the ratio between the input and output of the actuator is maintainedby selection of the gear ratios of the main and secondary drive paths tobe opposite in terms of direction and sufficiently different in terms ofabsolute ratio. The rotational speed of the output member 36 istherefore given by the equation: $\begin{matrix}{\omega_{out} = \quad {{\omega_{in}\left( {1/1} \right)}\left( {{1/30} - {1/40}} \right)}} \\{= \quad {{25/3}\quad {rpm}}}\end{matrix}$

As can be seen, the result is that regardless of whether a jam occursalong the main drive path or in the differential, the same gear ratio isapplied to the input drive in order to produce a constant output speedof the output member 36.

The substantially constant gear ratio is achieved by selecting the gearratios of the two drive paths to be opposite in terms of direction.andsufficiently different in ratio to achieve the requirement.

The description given above with regard to FIGS. 4 to 6 is a simplifiedview of the operation of the actuator. Each compound planetary epicyclichas a substantially different ratio to account for the different ratiosof the input differential according to each particular drive path. Onedrive is chosen with a negative ratio and one with a positive ratio withthe difference between the two being in proportion to that of the inputdifferential along its two drive paths. These ratios are selected alongwith the input differential to give constant output speed with respectto the input speed regardless of the path taken within the device. Inaddition, high gear reductions from input to output are achievable. Itwill be appreciated that, instead of the compound planetary epicyclicgearing for the output drives of the primary and secondary drive paths,other gearing may be used. For example, simple epicyclic reductiongearing arranged in series, can be used.

As can be seen from the drawings the output member 36 rests on thesecondary drive carrier member and therefore even if the output memberdoes seize to the carrier member drive will still be transmitted to theoutput member.

If a jam does occur within the actuator and subsequently clears orpartially clears the actuator will continue to operate with.an input tooutput ratio which remains substantially constant or unchanged.

What is claimed is:
 1. A geared rotary actuator having: a differentialgear unit having a drive input and first and second reduced outputs; anoutput driven member for connection to an external member to be drivenby the actuator; said second drive path includes an output carrier forcarrying the first drive path such that: a first drive path comprising afirst balanced planetary configuration coupling said first output of thedifferential gear unit to said output driven member; a second drive pathcomprising a second balanced planetary configuration; and an outputcarrier carrying said first and second balanced planetaryconfigurations; wherein said second balanced planetary configurationcouples said second output of the differential gear unit to said outputdriven member by way of said output carrier; and wherein the arrangementis such that: under normal conditions drive is transmitted from theinput drive to the output driven member via said differential gear unitand said first drive path; in response to jamming or binding of saidfirst drive path said first drive path and said second drive path arecaused to rotate en bloc thereby to transmit drive to said output,driven member via said differential gear unit and said second drivepath; and in response to jamming or binding of said differential gearunit, drive is transmitted to said output member via said differentialgear unit and both said first and second drive paths; the arrangementbeing further such that the gear ratio between said drive input and saidoutput driven member remains substantially the same.
 2. A geared rotaryactuator according to claim 1 wherein said second drive path includes anoutput carrier for carrying the first drive path such that in responseto jamming of said first drive path, said first drive path and saidsecond drive path are caused to rotate en bloc thereby to transmit driveto the output driven member.
 3. A geared rotary actuator according toclaim 1 where one of said drive paths has a negative ratio and the otherof said drive paths has a positive ratio, the difference in magnitude ofsaid ratios being in proposition to that of the differential gear untilalong said drive paths.
 4. A geared rotary actuator according to claim 3wherein said first and second drive paths each comprises a balancedplanetary configuration thereby to reduce the occurrence of skewing ofthe planetary gears under applied loading.
 5. A geared rotary actuatoraccording to claim 3 wherein said primary and secondary drive paths eachcomprises a balanced planetary configuration thereby to reduce theoccurrence of skewing of the planetary gears under applied loading.
 6. Ageared rotary actuator according to claim 5 wherein the balancedplanetary configuration includes a three planet/annulus gear assemblyfor each of the first and second drive paths.
 7. A geared rotaryactuator according to claim 5 wherein each assembly comprises end gearplanet/annulus gears which gears are substantially identical so that theforces thereon are substantially balanced.
 8. A geared rotary actuatoraccording to claim 1 wherein said selected ratio is greater than 50:1.9. A geared rotary actuator according to claim 1 wherein said selectedratio is greater than 200:1.
 10. A geared rotary actuator according toclaim 2 wherein said first and second drive paths each comprises abalanced planetary configuration thereby to reduce the occurrence ofskewing of the planetary gears under applied loading.